Fix EZP-22840: InvalidArgument on user/login with subtree role limitation

JIRA: https://jira.ez.no/browse/EZP-22840

Some roles are assigned to users/groups with a subtree limitation.
This will cause login (and possibly others) to fail, as the `$object` of SubtreeLimitation (siteaccess) is not be "compatible".

AFAICT In these cases evaluate should simply return `false`.